This invention relates generally to bicycles and, more particularly, to bicycle forks.
Bicycles have provided the world""s population with an important mode of transportation and pleasurable recreation for over 100 years. Because bicycles are propelled solely by the muscle power of the user, it is important that the bicycle be constructed of the lightest possible material which can adequately withstand the day-to-day stresses placed on the bicycle. Heretofore, the conventional wisdom has been that bicycles must generally be constructed from steels or materials of similar density. Many attempts have been made to construct bicycles from lighter weight materials, ut none of those efforts have been wholly successful.
One of the principal problems in constructing a bicycle from lightweight materials arises from the extreme stresses placed upon the fork portions of a bicycle. The front forks receive considerable impact and axial stresses applied to the bicycle by contact of the bicycle with rough terrain. Because bicycle forks are narrow and elongate, they are especially subject to deformation when constructed from materials that are weaker than steel.
Some manufacturers have resorted to constructing bicycle forks from special alloys and material having a low density and steel-like strength. Materials such as titanium, magnesium and carbon fiber composites fall within this category. Unfortunately, bicycle forks made from such materials tend to be expensive.
Accordingly, there is a need for a lightweight bicycle fork which avoids the problems the prior art.
The invention satisfies this need. The invention is a bicycle fork comprising (a) a crown having a central portion, a pair of opposed side portions, a top surface and a bottom surface, (b) a stem having a top end and a bottom end, the bottom end of the stem being connected to the central portion of the crown such that the stem projects upwardly above the top surface of the crown, and (c) a pair of opposed tubular struts, each having a top end and a bottom end, the top end of each strut being mechanically attached to one of the opposed side portions of the crown such that the struts project downwardly from the bottom surface of the crown in parallel to one another. Each strut is made from a lightweight material, and each strut is preferably internally reinforced with a reinforcing web to strengthen the strut with respect to axial and lateral forces.
In a preferred embodiment, a pair of spaced-apart bores are provided in the pair of opposed side portions of the crown and each strut is secured within a respective bore by a threadably attached end cap, such mechanical attachment of the forks to the crown rigidly retaining the struts within the crown without need of welding or other such attachment means. In a further preferred embodiment, both struts are prevented from rotating within the bores by longitudinal ribs which nest within corresponding grooves in each bore.
The invention is ideally suited for bicycle forks constructed from aluminum, and other such materials.
The invention has been found to provide an inexpensive bicycle fork having considerable strength, but which weighs markedly less than conventional steel forks.